Twins were selected from Cohort I if they had data on lifetime DSM-III-R alcohol dependence (AD) symptoms assessed during interview and variables used to code reproductive onset, which were included in the 1988–89 questionnaire, but omitted from interview. Of 5879 twins completing 1988–89 questionnaire and interview assessments, 5514 (94%) had data on both AD and reproductive onset, including 3634 female and 1880 male respondents. Age at interview of selected twins ranged from 28 to 93 [M (SD) = 44.68 (12.37)].
